A typical industrial gas turbine engine has multiple combustion chambers in a circumferential configuration about the engine shaft. For each combustion chamber there is normally a transition duct, also referred to as a transition piece, through which the hot combustion exhaust flow is carried from each combustion chamber to the inlet of the turbine section. With the plurality of combustion chambers arranged about a central axis of the gas turbine engine, the transition pieces are radially arranged about the turbine axis and comprise outlet ends that converge to form an annular inflow to the turbine inlet. Each transition piece is joined via a sealing arrangement to the turbine inlet section, which is at the front end of the row one vane segment. These and adjoining components experience thermal expansion, thermal stresses and vibrational forces resulting from combustion dynamics, all of which are known to adversely affect performance of numerous components, including the seals. Consequently, numerous seal designs have been proposed to find an improved balance between the seal cost, reliability, durability, installation and repair costs and adverse effects on adjacent components.
One or more turbine vanes mounted between outer and inner curved platforms is called a nozzle. Retainer rings retain a set of nozzles in a circular array for each stage of the turbine. Upper and lower seals on an exit frame of each transition piece seal against respective outer and inner retainer rings of the first stage nozzles to reduce leakage between the combustion and turbine sections of the engine.
Multiple such seals are part of the interface between the exit end of each transition piece and the inlet of the turbine section. Upper and lower seals on an exit frame of each transition piece form part of the sealing structure between the transition piece and the turbine inlet. Also to reduce leakage between the combustion and turbine sections of the engine, additional seals are provided in the interface structure between the exit frame and outer and inner retainer rings of the first stage nozzles. These seals conventionally have sufficient clearance in their slots to accommodate relative dynamic motion and differential thermal expansion between the exit frame and the retainer ring. For this reason, such seals may be called “floating seals”. However, such clearance increases gas leakage across the seal, thereby reducing engine efficiency. The initial close tolerances of newly installed floating seals are degraded as a result of wear over the component life. This results in larger gaps through which compressed air enters the hot gas path. This, in turn, is expected to reduce efficiency and may lead to higher emissions of nitrogen-containing by-products.